This invention relates to an endoscope whose illumination optical system has been improved.
In recent years, the number of foreground subjects to be observed by an endoscope has grown in the fields of medical treatment and manufacturing industries, and has assumed extremely diversified forms. Sometimes a wide angle is preferred, depending on the type of foreground subject to be examined. As a result, the range of the illumination carried out by the endoscope illumination apparatus has to be widened. To meet this requirement, various attempts, including the use of a wide angle lens, have been made. However, none of the proposals advanced to date have been able to realize a sufficiently wide illumination angle. Moreover, the illumination by the conventional illumination apparatus is brightest at its center and grows progressively darker toward its periphery. When, therefore, observation was made of the inner walls of, for example, the alimentary canal or intestines which are located at the peripheral portions of the illumination range of the apparatus, it was difficult to distinctly observe the subject due to the great darkness prevailing over the peripheral portions. In such a case, the light at the center of the illumination range of the illumination apparatus made no contribution to the observation of the above-mentioned inner walls and was simply wasted. Therefore, the conventional illumination apparatus is accompanied with the drawback that its illumination efficiency was considerably unsatisfactory.